1. Field of the Invention
This invention pertains generally to devices for measuring acceleration, and more particularly to a micromachined accelerometer employing a fluid proof mass.
2. Description of the Background Art
Conventional micromachined accelerometers employ a solid constrained proof mass. In such accelerometers, the proof mass typically comprises a section of silicon supported from a frame by thin silicon tethers or cantilevers. One class of such devices employs strain measurement in the constraining tethers or cantilevers to sense inertial forces on the proof mass. Strain measurement is typically achieved through the use of implanted or diffused piezoresistors in the constraints. This is the principle employed in piezoresistive cantilevered or tethered accelerometers. Another class of devices senses displacement of the constrained proof mass by capacitive transduction, and often employs force-feedback techniques to improve sensitivity. Additionally, conventional solid proof mass micromachined accelerometers provide only one axis of inertial sensitivity; that is, only one degree of freedom. While monolithic devices having two degrees of freedom have been considered, none have achieved commercial viability.
While macroscopic sensors have been built with fluid proof mass as an assembly of components such as pressure sensors and rigid tubing filled with fluid, micro-fabricated accelerometers employing a fluid proof mass have not been heretofore developed. Additionally, there are no known monolithic or micromachined accelerometers with three linear degrees of freedom. Nor have monolithic or micromachined accelerometers with combined linear and rotational acceleration sensitivity been heretofore developed. Therefore, there is a need for a sensitive micromachined accelerometer having multiple linear degrees of freedom and which can be used to measure linear and rotational acceleration. The present invention satisfies those needs, as well as others, and overcomes the deficiencies in devices heretofore developed.